Protection of pump surfaces



Jun 17, 1947.

D. VAN DER MERWE HAARHOFF 2,422,412

PROTECTION OF PUMP SURFACES Original Filed May 16, 1939 2 Sheets-Sheet 1June 17, 1947 D. VAN DER MERWE HAARHOFF 2,422,412

PROTECTION OF PUMP SURFACES Original Filed May 16, 1939 2 Sheets-Sheet 2A Z6 27 I 2 9 14. 26 I F a I Wan a.

Patented June 17, 1947 UNITED STATES FTENT OFFICE ROTECTION OF PUMPSUBFAQES Orig nal application May 16, 1939, Serial No.

Divided and this application February 2%, 1942, Serial No. 432,137. Inthe Union of South Africa December 18, 1937 3 Claims. 1

This application is a division of application Serial No. 274,055 filedMay 16, 1939.

The present invention relates to centrifugal pumps for transportingliquid or pulp containing sand, gravel or like abrasive matter, and itsobject is to reduce the erosive effect of the liquid or pulp on theimpeller and other portions of the pump exposed thereto. This erosiveeffect is very great when pumping under considerable pressures, even incases where the proportion of abrasive matter is small.

According to the invention, in a centrifugal pump for transportin liquidor pulp containing sand, gravel or like abrasive matter, exposed interior portions of the pump are provided with a wear-resistant surfacelayer comprising a resiliently yielding bonding medium comprisingrubber, and hard and tough wear-resistant granular material distributedin said medium.

The wear-resistant material may consist, for example, of quartz grit,emery, Carborundum, corundum, flint, bauxite carbides, silicides andlike natural or synthetic substances of a hard and tough character whichare commonly used as abrasives. The size of the rains is not criticaland the best size for each kind of pump can readily be found byexperiment.

It appears that in the surface layer of the invention the hard and toughmaterial covers and shields the rubber and thus decreases to a substantial extent wear of the rubber; whilst the elasticity of the rubberdecreases to a Substantial extent wear of the hard material, as itpermits the hard particles to recede when exposed to the impact ofabrasive grains and thus to diminish the abrasive force acting upon themand thereupon to return to their original positions; and it has beenproved that the surface layer of the invention wears off, under thesameconditions, at a very considerably slower rate than the knowncoatings consisting of rubber or of hard and tough wear-resistantmaterial without an elastic rubber bond.

The wear-resistant surface layer of the invention may be provided bypreformed sheets or rings which are subsequently secured to the pumpportions which are to be protected. A very important advantage of theinvention, however, consists in that it permits of building up in situ awearsresistant surface layer firmly attached to the exposed pumpportions without the necessity of heating such portions or applyingpressure.

Accordingly the invention also comprises a method for protecting exposedportions of centrifugal pumps subjected to abrasion which c0nsists inapplying the aforesaid surface layer by building it up on the exposedportions with the use Of plastic and/or liquid material.

The best manner of carrying out this method will depend on the nature ofthe pump portion which is to be coated, on the intended thickness of thewear-resistant surface layer and on other factors, and may be varied inits details to suit any particular case.

In its preferred form, the method comprises thesteps of preparing thepump portion to receive the surface layer, for instance, by applying atleast one thin primer coat; applying to the resulting thin coat, whileit is still in an adhesive condition, one or more coats of a solutioncontaining cold vulcanizin rubber, applying a coat of primer solution onto the rubber coat or on to the last rubber coat while the lat ter isstill in an adhesive condition, sprinkling the granular material on tothe primer coat, and applying, preferably immediately, to the granularmaterial, a further coat of primer solution, the last said two primercoats promoting adherence bet-ween the granular material and the'rubher.The thickness of the surface layer may be increased by increasing thenumber of rubber coats and, if desired, also the number of coats ofgranular material. In pumps the interior portions of which are exposedto high pressures, the thickness of the resistant surface layer shouldnot exceed 3% of an inch.

If the pump portion to be protected consists of a copper alloy such asbronze it is preferred to coat it with a thin layer of pure iron orother ferrous metal, as by spraying; and to apply the protective surfacelayer in the aforesaid manner to the iron coating.

The term solution containing cold vulcanizing rubber is intended to meanthroughout the specification and claims a solution which, uponevaporation of the solvent, leaves a coating comprising solid rubberwhich is either fully vulcanized or vulcanizes by itself within a shorttime without artificial application of heat.

Such solutions generally comprise rubber, sulphur, an activator, anaccelerator and fillers and may be of the latex or of the benzol type.The manner of compounding such solutions so as to produce grades ofrubber differing in elasticity, hardness and the like is well known inthe art. For example, a latex solution suitable to yield, on evaporationof the water, a very tough and highly resilient rubber may compriseabout 50% of rubber, from 5% to 2% and preferably 3% sulphur, 3% zincoxide and an ultra-accelerator.

may comprise natural or artificial resins, chlorinated rubber or rubberderivatives of resinous character, bitumen or the like and/or rubber andsuitable curing or vulcanizing agents. Suitable primers are marketed,for example under the trade names Selfvulc M Primer and Malacca 101Primer.

In another form the method of the invention comprises the steps ofmixing a liquid or plastic composition containing e. g. about 40% to 60%of cold vulcanizing rubber and a suitable solvent with the granularmaterial in, for example, equal volumes, applying the resulting mixtureto the pump portion, which is previously coated with primer, and coatingthe thus produced surface, while it is still in adhesive condition, witha coat of primer solution. This manner of applying the protectivecoating is particularly suitable when coatings of greater thickness aredesirable.

In another way of carrying out the method of the inventionnon-self-vulcanizing rubber solutions are used and the coats arevulcanized by exposing them to sulphur chloride or in a similar manner.These solutions may be used, except for the vulcanization step, insubstantially the same way as aforedescribed with reference to solutionscontaining cold vulcanizing rubber.

The rubber solutions may be applied by painting, spraying, dipping or inany other known manner suitable for the purpose of the invention.

For attaining a high degree of resistance against abrasion it isessential that the grains of the wear-resistant material form a materialportion of the exposed surface of the wear-resistant layer; that they beevenly distributed and be spaced from one another and that each grain beelastically cushioned by the rubber.

The term rubber is intended to include rubber and similar substancessuitable to constitute a rubber-like highly resilient, tough, bondingmaterial.

In some cases it is advantageous to interpose between the pump portionto be protected and the wear-resistant surface layer a thin preformedsheet of rubber and more particularly sponge rubber. Said preformedsheet may be secured to the pump portion by a suitable cement, e. g.primer solution; the wear-resistant surface layer being built up on saidsheet according to the aforedescribed method of the invention.

Embodiments of the invention will now be described, by way of example,reference being made to the accompanying drawings comprising Figures Ito IV.

Figure I is a cross-section in a vertical plane through part of amulti-stage centrifugal pump for lifting gritty liquid against aconsiderable head.

Figure II is a cross-section through portion of the impeller 3 of thepump of Figure I along the line IIII.

Figure III is a cross-section through portion of the impeller 2 of thepump of Figure I along the line IIIIII.

Figure IV is a cross-section in a vertical plane through a centrifugalpump for transporting sand The part of the multi-stage centrifugalpump 4shown in Figure I has two impellers 2, 3 feathered on a common shaft 4which is supported in bearings arranged outside the pump casing. Thegritty liquid to be pumped enters at 5 into the first 5 impeller 2. Theliquid discharged by the first impeller 2 enters the diifuser guide 6which leads the liquid into the diffuser passage 1 which in turn leadsthe liquid inwardly to the eye of the second impeller 3. The liquiddischarged by the second impeller 3 enters the second diffuser guide 8from which it passes out of the pump via the delivery pipe 9. The shaft4 is prevented from being moved in an endwise direction by the axialthrust exerted by the liquid, by the provision of a stationary seatingplate H) which is rigidly secured to the casing of the pump and bears atits periphery against a balancing disc H which is fixed on and revolveswith the shaft E. Renewable metal wearing rings I2 and [3 are inset intothe plate iii and disc I I respectively. The space Hi enclosed by ID andII is supplied with liquid under pressure from the second impeller 3through the clearance between the suction boss of the impeller 3 and theboss of the seating plate Hl.

This liquid passes out between the peripheries of ii) and ii into thebalancing chamber l5 and r then through a connecting pipe back to thesuction end of the pump. The balancing disc ii is extended to form awearing sleeve I6 which fits over the shaft 4 where it passes throughthe packing l1. 7

Due to the flow of gritty liquid through the pump, the portions of thepump exposed thereto will rapidly become worn away when constructed ofmetal as is the usual practice. Wear is particularly rapid in placeswhere the liquid has a high velocity and/or pressure, and the usualpractice is to arrange that those portions subjected to rapid Wear arereplaceable e. g. the impellers 2, 3 wearing ring l2, l3 and wearingsleeve l6. For the same reason the sealing surfaces leading'from theimpellers to the diffusers are formed by replaceable eye rings is andthe sealing surfaces leading from the diffusers to the impellers areformed by replaceable suction rings it. These exposed portions requireparticular protection against erosion. v a

The aforesaid portions or some of them are provided with wear-resistantsurface layers 20 of the specified kind. Said surface layers may bebuilt up as follows: The exposed pump portions are first cleaned withpetrol, benzine or other cleansing agent, or by sandblasting. Theirclean metal surface is then given three coats of a primer solution,about an hour being allowed between each coat to permit it to set. Theresulting primer layer is then given three coats of a solutioncontaining cold vulcanizing rubber. Each coat is allowed to set beforethe next is applied, about 2 /2 hours being usually sufllcient.Thereupon a coat of primer solution is applied to the last rubber coatand granular material is sprinkled onto the primer while the latter isstill in an adhesive condition; finally, a further coat of primersolution is applied on top of the granularmaterial in order toincorporate it firmly with the rubber. When the exposed pump portionsare easily accessible, as for example, the outside of an impeller, thesuccessive coats may be applied by painting; when they are not easilyaccessible, as for example, the inside of an impeller, the coats may beapplied by spraying or by submerging the part successively in thevarious coating liquids, one of which contains the granular material insuspension.

When two exposed pump portions bear upon .each other, as for example,the portion I9 and the impeller inlet boss, it is preferred to provideonly one of them, preferably the one presenting a concave surface, witha wear-resistant surface layer 20 of the specified kind and to providethe other with a coating 2| consisting of ordinary rubber.

As indicated in Figure I, it is preferred to apply wear-resistantsurface layers 20 to substantially all the interior portions of the pumpincluding the diffuser passages and the discharge pipe 9. The impellervanes 22 (Figure III) may have a wear-resistant surface layer 20 appliedto both their surfaces but it is generally sufficient to apply suchlayer tothe working surface of the impeller only; in this case thesurface layer 20 should, however, extend over the top of the vanes asindicated in Figure III.

Figure IV shows a sand pump having a suction passage 23 and a deliverypassage 24, the sand pulp being transported from 23 to 24 by an impeller25 secured to a shaft 26 provided with a wearing sleeve 21, where itpasses through the packing 28. The impeller 25, suction passage 23,delivery passage 24 and the inner walls of the pump casing 29 areprotected against erosion by wear-resistant surface layers 20 of thespecified kind which may be produced as described in connection withFigure I. In addition the wearing sleeve 2! is grooved at one side ofthe packing 28 and a wear-resistant surface layer of the specified kindis built up in the groove as indicated at 30 so as to prevent wear dueto sandy water leaking along the sleeve 21.

I claim:

1. A method of protecting a surface subjected to abrasion, comprisingthe steps of applying to solution, applying to the outermost rubber coatat least one further coat of a primer solution, sprinkling the outermostof said further coats, whilst it is still in adhesive condition, withhard and tough Wear-resistant granular material, and applying to saidwear-resistant material at least one further coat of primer solution.

2. The method claimed in claim 1, in which the hard and tough granularwear-resistant material belongs to the group consisting of emery,Carborundum, corundum, flint, and siliceous abrasive materials.

3. A method of providing centrifugal pumps, for transporting liquid orpulp, containing sand, gravel and the like abrasive matter, withwearresistant working surfaces, comprising the steps of applying toexposed inner portions of such pumps at least one coat of primersolution which is suitable to bond rubber to metal and is also suitableto bond hard and tough granular material to rubber, applying to theoutermost primer coat when the latter is in an adhesive condition atleast one coat of cold vulcanizing rubber solution, applying to theoutermost rubber coat thus produced at least one further coat of aprimer solution, sprinkling the outermost of said further coats whilstit is in an adhesive condition, with hard and tough wear-resistantgranular material, and applying to said wear-resistant material at leastone further coat of primer solution.

DANIEL VANVDER MERWE HAARHOFF.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,165,955 Van der M.HaarhoffnJuly 11, 1939 1,254,156 Parsons Jan. 22, 1918 1,271,072 ParsonsJuly 2, 1918 2,290,905 Butler July 28, 1942 2,310,629 I-Iaarhoff Feb. 9,1943

